Thermal ablation of tissue can be performed to remove diseased tissue, such as precancerous or cancerous tissue. For example, thermal ablation has been used in the treatment of Barrett's esophagus, which is a precancerous condition. Thermal ablation can also be performed to remove old tissue and to provide a new surface to support growth of new tissue. Typically, thermal ablation is performed by passing an electrode through a working channel of an endoscope, placing the electrode near the tissue region to be treated and applying radio-frequency (RF) energy to the electrode. An advantage of this technique is that the procedure can be performed under direct visualization. A disadvantage of this technique is that the diameter of the electrode is necessarily limited by the small diameter of the working channel of the endoscope. As a result, the electrode can only treat a small area of the tissue at a time.
In some precancerous conditions that may be treatable via thermal ablation, the area to be treated is relatively large with respect to the electrode, resulting in very long procedure times, irregular or incomplete ablation, and variations in the depth of the ablative effect. The inability to control sufficiently the depth of the ablation procedure can lead to charring or perforation of the tissue or a failure to reduce significantly the number of precancerous cells to a sufficiently low level.
Attempts have been made to provide large electrodes to overcome these limitations. For example, electrodes have been provided on expandable surfaces such as balloons. These apparatuses, however, have been limited to some extent by the diameter of the accessory channel of an endoscope.